1. Field of the Invention
This invention relates to a method and apparatus for inspecting fiberoptic communication paths. In particular it relates to the field of optical time domain reflectometry (ODTR) and to the correlation of optical and physical distances from an observer to a reflective event.
2. Description of the Prior Art
Conventional ODTR methods that are employed for the detection of splice points or discontinuities in optical fibers rely on the injection of optical energy at a launch point, and the reception of reflected or backscattered light by a receiver. A common reason to dispatch a field worker is a broken or damaged cable that appears to the ODTR instrument as a short fiber. For the most part, reflective events are the result of an interface of glass and air, and are therefore characteristic of many breaks. It is the reflective property of the discontinuity that can be used to determine the distance from a given point to the discontinuity without having to break the fiber mid-span.
An OTDR instrument evaluates a characteristic of the reflected light to determine the optical distance to a reflective event. Once the optical distance to an event has been determined, a worker must physically locate the break. Because the optical and physical distances to an event are often quite different, it would be advantageous for a worker in the field who is seeking an anomaly to check its location from time to time. In order to do this using conventional OTDR, it is necessary to attach a field instrument to the fiber. Because of fused splices, this may not be feasible. Fiber in the Loop (FITL) deployments call for a multidrop, rather than a point-to-point architecture as exists in today's inter-toll plant. Applying conventional ODTR methods to an FITL installation results in a confusing, and for the most part, unintelligible picture. It would be highly desirable for a field worker to rapidly access feeder fibers at multidrop points, look down the branches, and "see" reflective anomalies, so that a defect in the fiber can be expeditiously located and repaired.